U.S. Pat. Nos. 3,845,018 and 3,879,349 disclose certain acetylene end-capped polyimide oligomers. Moldings prepared from such resin have excellent physical properties which are largely retained at temperatures as high as 316.degree. C. (600.degree. F.).
These oligomers have very high melting points above 210.degree. C. and require extended heating cycles to crosslink the resins to develop optimum physical properties. For these reasons, the molding cycles are long and moldings prepared from such oligomers are expensive.
The prior art discloses that it is necessary to employ high boiling solvents such as dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) to prepare these oligomers. Unless special precautions are employed to remove such solvents from the oligomers, residual solvent evolves when the oligomers are molded. This action frequently causes the moldings to crack and/or fracture. It also is observed that large moldings sometimes crack when they are post cured by being heated to 371.degree. C. (700.degree. F.) for extended periods of time, due to stresses caused by large changes in thermal expansion.
For the above reasons, there is a need in the art for improved processes for molding acetylene end-capped polyimide oligomers.